Inter-cell interference (ICI) may be considered to be interference at a cell due to transmissions originating in another cell. Usually, ICI occurs between adjacent cells of a communications system. As an example, relatively high-powered transmissions to and from a cell edge user (CEU) operating in a first cell may cause more interference to adjacent cells utilizing the same operating frequency than relatively lower-powered transmissions to and from a cell center user (CCU) operating in the first cell to adjacent cells utilizing the same operating frequency due to correspondingly higher power levels of the transmissions to and from the CEU.
FIG. 1 illustrates a prior art communications system 100. Communications system 100 includes a first evolved NodeB (eNB) 105 and a second eNB 115. An eNB (also commonly referred to as a base station, communications controller, NodeB, and so forth) may be in communications with User Equipment (UE) operating within its coverage area. For example, eNB 105 may have a coverage area illustrated in FIG. 1 as hexagon 110, while eNB 115 may have a coverage area illustrated as hexagon 120. Operating within hexagon 110 may be a first UE 125 and a second UE 130. A UE may also be commonly referred to as a mobile station, user, terminal, subscriber, and so on).
A coverage area of an eNB (or more generally, a cell of an eNB) may be categorized based upon a distance (in an electrical distance sense wherein a more distant UE may have receive greater signal strength than a closer UE due to factors such as shadowing, line of sight, height, and so on) of a UE to the eNB. For example, coverage area of eNB 105 (i.e., hexagon 110) may be categorized into two regions, with a first region being a cell center region (shown as circle 135) and a cell edge region (portions of hexagon 110 outside of circle 135, shown as region 140). Normally, with downlink fractional frequency reuse inter-cell interference coordination (ICIC), UEs operating within a cell center region, such as UE 125, may receive transmissions made at a lower power level than UEs operating outside of a cell center region, such as UE 130, due to their closer proximity to the eNB serving the coverage area.
Furthermore, since transmissions made by UEs (i.e., uplink transmissions) operating with a cell edge region, such as UE 130, are usually made at higher power levels and the UEs are also located closer to neighboring (e.g., adjacent) eNBs, the transmissions may cause more interference to the neighboring eNBs. For downlink transmissions, UEs in a first eNB (e.g., a serving eNB) that are located closer to a neighboring eNB (i.e., an adjacent eNB) may experience high interference from transmissions of the neighboring eNB than UEs operating in a cell center region of the first eNB.
One form of ICIC is fractional frequency reuse (FFR) ICIC. In FFR ICIC, available time and/or frequency resources may be divided into multiple parts, also commonly referred to as a FFR pattern or frequency reuse pattern, which may be allocated to different transmitters. The transmitters may then transmit only during times and/or in frequencies associated with their allocated time and/or frequency part(s), or transmit with different power densities in different time and/or frequency parts according to a predefined power density mask. Assignment of the time and/or frequency parts may be made so that adjacent and/or close transmitters cause little or no interference to one another and/or receivers. As an example, adjacent transmitters may be assigned different time and/or frequency part(s) so that their transmissions do not overlap either in time and/or frequency.
The FFR ICIC technique used may be referred by the number of parts that the available is divided into. As an example, FFR with reuse-2 would divide the available resources into two parts that may be assigned to transmitters in an attempt to reduce interference. Similarly, FFR with reuse-3 would divide the available resources into three parts, while FFR with reuse-1 would not divide the available resources at all and may be indicative of non-FFR operation.
It is widely considered that ICI management will be a key technology for enhancing the performance of Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant communications systems, for example, and overall UE experience. Therefore, there is a need for ICI reducing techniques, of which, ICIC is one form. ICIC is a simple and efficient ICI management scheme. Generally, ICIC attempts to reduce and/or control ICI through the use of radio resource management (RRM) methods. Typically, ICIC takes into account information from multiple cells, such as neighboring cells, to control inter-cell interference. A usual ICIC strategy may be to determine resources available at a cell, which may then be scheduled (i.e., allocated) to users. ICIC in Orthogonal Frequency Division Multiple Access (OFDMA) communications systems, such as 3GPP LTE communications systems, have received considerable study.
A persistent challenge to communications systems is the change in operating conditions over time. For example, cell loading may change over time, UE distribution geometries may change over time, number of scheduled UEs may change over time, and so forth. As the operating conditions change, an ICIC mode that yielded good performance under a first set of operating conditions may no longer provide good performance under a second, different set of operating conditions. Additionally, operating conditions may vary on a geographical basis, and an ICIC mode that works well in one area may not work as well in another. Therefore, there is a need for a system and method that allows for ICIC mode self-optimization at a variety of different levels and/or granularities to meet changing operating conditions in the communications system.